3.2 Options Controlling the Kind of Output

Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order. GCC is capable of
preprocessing and compiling several files either into several
assembler input files, or into one assembler input file; then each
assembler input file produces an object file, and linking combines all
the object files (those newly compiled, and those specified as input)
into an executable file.

For any given input file, the file name suffix determines what kind of
compilation is done:

file.c

C source code that must be preprocessed.

file.i

C source code that should not be preprocessed.

file.ii

C++ source code that should not be preprocessed.

file.m

Objective-C source code. Note that you must link with the libobjc
library to make an Objective-C program work.

file.mi

Objective-C source code that should not be preprocessed.

file.mm

file.M

Objective-C++ source code. Note that you must link with the libobjc
library to make an Objective-C++ program work. Note that ‘.M’ refers
to a literal capital M.

file.mii

Objective-C++ source code that should not be preprocessed.

file.h

C, C++, Objective-C or Objective-C++ header file to be turned into a
precompiled header (default), or C, C++ header file to be turned into an
Ada spec (via the -fdump-ada-spec switch).

file.cc

file.cp

file.cxx

file.cpp

file.CPP

file.c++

file.C

C++ source code that must be preprocessed. Note that in ‘.cxx’,
the last two letters must both be literally ‘x’. Likewise,
‘.C’ refers to a literal capital C.

file.mm

file.M

Objective-C++ source code that must be preprocessed.

file.mii

Objective-C++ source code that should not be preprocessed.

file.hh

file.H

file.hp

file.hxx

file.hpp

file.HPP

file.h++

file.tcc

C++ header file to be turned into a precompiled header or Ada spec.

file.f

file.for

file.ftn

Fixed form Fortran source code that should not be preprocessed.

file.F

file.FOR

file.fpp

file.FPP

file.FTN

Fixed form Fortran source code that must be preprocessed (with the traditional
preprocessor).

file.f90

file.f95

file.f03

file.f08

Free form Fortran source code that should not be preprocessed.

file.F90

file.F95

file.F03

file.F08

Free form Fortran source code that must be preprocessed (with the
traditional preprocessor).

file.go

Go source code.

file.ads

Ada source code file that contains a library unit declaration (a
declaration of a package, subprogram, or generic, or a generic
instantiation), or a library unit renaming declaration (a package,
generic, or subprogram renaming declaration). Such files are also
called specs.

file.adb

Ada source code file containing a library unit body (a subprogram or
package body). Such files are also called bodies.

file.s

Assembler code.

file.S

file.sx

Assembler code that must be preprocessed.

other

An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.

You can specify the input language explicitly with the -x option:

-x language

Specify explicitly the language for the following input files
(rather than letting the compiler choose a default based on the file
name suffix). This option applies to all following input files until
the next -x option. Possible values for language are:

Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if -x
has not been used at all).

-pass-exit-codes

Normally the gcc program exits with the code of 1 if any
phase of the compiler returns a non-success return code. If you specify
-pass-exit-codes, the gcc program instead returns with
the numerically highest error produced by any phase returning an error
indication. The C, C++, and Fortran front ends return 4 if an internal
compiler error is encountered.

If you only want some of the stages of compilation, you can use
-x (or filename suffixes) to tell gcc where to start, and
one of the options -c, -S, or -E to say where
gcc is to stop. Note that some combinations (for example,
‘-x cpp-output -E’) instruct gcc to do nothing at all.

-c

Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.

By default, the object file name for a source file is made by replacing
the suffix ‘.c’, ‘.i’, ‘.s’, etc., with ‘.o’.

Unrecognized input files, not requiring compilation or assembly, are
ignored.

-S

Stop after the stage of compilation proper; do not assemble. The output
is in the form of an assembler code file for each non-assembler input
file specified.

By default, the assembler file name for a source file is made by
replacing the suffix ‘.c’, ‘.i’, etc., with ‘.s’.

Input files that don't require compilation are ignored.

-E

Stop after the preprocessing stage; do not run the compiler proper. The
output is in the form of preprocessed source code, which is sent to the
standard output.

Input files that don't require preprocessing are ignored.

-o file

Place output in file file. This applies to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.

If -o is not specified, the default is to put an executable
file in a.out, the object file for
source.suffix in source.o, its
assembler file in source.s, a precompiled header file in
source.suffix.gch, and all preprocessed C source on
standard output.

-v

Print (on standard error output) the commands executed to run the stages
of compilation. Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.

-###

Like -v except the commands are not executed and arguments
are quoted unless they contain only alphanumeric characters or ./-_.
This is useful for shell scripts to capture the driver-generated command lines.

-pipe

Use pipes rather than temporary files for communication between the
various stages of compilation. This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
no trouble.

--help

Print (on the standard output) a description of the command-line options
understood by gcc. If the -v option is also specified
then --help is also passed on to the various processes
invoked by gcc, so that they can display the command-line options
they accept. If the -Wextra option has also been specified
(prior to the --help option), then command-line options that
have no documentation associated with them are also displayed.

--target-help

Print (on the standard output) a description of target-specific command-line
options for each tool. For some targets extra target-specific
information may also be printed.

--help={class|[^]qualifier}[,...]

Print (on the standard output) a description of the command-line
options understood by the compiler that fit into all specified classes
and qualifiers. These are the supported classes:

‘optimizers’

Display all of the optimization options supported by the
compiler.

‘warnings’

Display all of the options controlling warning messages
produced by the compiler.

‘target’

Display target-specific options. Unlike the
--target-help option however, target-specific options of the
linker and assembler are not displayed. This is because those
tools do not currently support the extended --help= syntax.

‘params’

Display the values recognized by the --param
option.

language

Display the options supported for language, where
language is the name of one of the languages supported in this
version of GCC.

‘common’

Display the options that are common to all languages.

These are the supported qualifiers:

‘undocumented’

Display only those options that are undocumented.

‘joined’

Display options taking an argument that appears after an equal
sign in the same continuous piece of text, such as:
‘--help=target’.

‘separate’

Display options taking an argument that appears as a separate word
following the original option, such as: ‘-o output-file’.

Thus for example to display all the undocumented target-specific
switches supported by the compiler, use:

--help=target,undocumented

The sense of a qualifier can be inverted by prefixing it with the
‘^’ character, so for example to display all binary warning
options (i.e., ones that are either on or off and that do not take an
argument) that have a description, use:

--help=warnings,^joined,^undocumented

The argument to --help= should not consist solely of inverted
qualifiers.

Combining several classes is possible, although this usually
restricts the output so much that there is nothing to display. One
case where it does work, however, is when one of the classes is
target. For example, to display all the target-specific
optimization options, use:

--help=target,optimizers

The --help= option can be repeated on the command line. Each
successive use displays its requested class of options, skipping
those that have already been displayed.

If the -Q option appears on the command line before the
--help= option, then the descriptive text displayed by
--help= is changed. Instead of describing the displayed
options, an indication is given as to whether the option is enabled,
disabled or set to a specific value (assuming that the compiler
knows this at the point where the --help= option is used).

Do not expand any symbolic links, resolve references to ‘/../’
or ‘/./’, or make the path absolute when generating a relative
prefix.

--version

Display the version number and copyrights of the invoked GCC.

-wrapper

Invoke all subcommands under a wrapper program. The name of the
wrapper program and its parameters are passed as a comma separated
list.

gcc -c t.c -wrapper gdb,--args

This invokes all subprograms of gcc under
‘gdb --args’, thus the invocation of cc1 is
‘gdb --args cc1 ...’.

-fplugin=name.so

Load the plugin code in file name.so, assumed to be a
shared object to be dlopen'd by the compiler. The base name of
the shared object file is used to identify the plugin for the
purposes of argument parsing (See
-fplugin-arg-name-key=value below).
Each plugin should define the callback functions specified in the
Plugins API.

-fplugin-arg-name-key=value

Define an argument called key with a value of value
for the plugin called name.

For input files in any language, generate corresponding Go
declarations in file. This generates Go const,
type, var, and func declarations which may be a
useful way to start writing a Go interface to code written in some
other language.

@file

Read command-line options from file. The options read are
inserted in place of the original @file option. If file
does not exist, or cannot be read, then the option will be treated
literally, and not removed.

Options in file are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character (including a
backslash) may be included by prefixing the character to be included
with a backslash. The file may itself contain additional
@file options; any such options will be processed recursively.